1. The Field of the Invention
The invention relates generally to emission devices employing a display means to produce an image. More specifically, the present invention relates to an optical emission device employing thermionic elements constructed with solid-state semiconductor device, micromachining, or microelectromechanical (MEM) fabrication techniques in combination with corresponding display means.
2. The Background Art
The development of television necessarily led to the parallel development of display devices. The classic display device utilizes cathode ray tubes ("CRT"). Initially, with black and white television, a single cathode gun located inside a cathode ray tube was used to project the desired signal to the phosphor coating on the picture tube. The phosphor coating, in turn, was illuminated as dictated by the signal received, thus producing the monochrome, or grayscale, images seen by an observer.
Color display technology operates in similar fashion but requires a cathode ray tube which employs a series of guns. Each gun emits an electron emission which illuminates a different color of phosphor on the display screen. Typically, three guns are used to illuminate red, green, and blue phosphors. By using red, green, and blue in varying combinations and intensities, any color may be achieved. This process is often referred to as the additive process of producing color.
As might be expected, however, CRT display systems have certain drawbacks. For example, CRTs are limited in the size of picture which can be displayed with acceptable quality. This is because increasing the picture size requires greater electron emission by the guns. At some point, increasing the picture size will exceed the capability of the guns to produce an acceptable picture. Increasing the picture size will at some point also exceed practical weight limitations for fabrication. Furthermore, CRTs require substantial space for implementation. In today's ever expanding display market, larger displays produced by smaller sized devices are desired features in a display system.
The advent of computers and a variety of other technologies also led to additional development in the area of displays. Today, home theater systems, camcorders, graphics systems, virtual reality systems, commercial transportation systems, cable, telephone, interactive media services, personal projections systems, personal digital assistants, virtual reality driven materials handling systems, automotive global positioning systems, and a variety of other systems in various fields of information display as well as television and computers all require display technology to operate. Such demand has naturally led to certain advancements in the field.
One such advancement is the liquid crystal display ("LCD"). The LCD was initially developed primarily for use in calculator and watch displays. More recently LCDs using a flat panel design have been implemented for television, lap top computers, and other applications. LCDs have had some success in providing a thinner screen in space restrictive applications. Unfortunately, these LCD display systems exhibit a number of major drawbacks, including excessive manufacturing costs, limited large screen capabilities, backlighting requirements, viewing angle limitations, and operating temperature limitations.
Other flat panel display technologies are also developing. Among these is the so called field emission display (FED). FEDs rely on the field emission from pointed tips under high electric fields. Unfortunately, FEDs also exhibit certain undesirable characteristics such as complex manufacturing and reliability concerns.
In the 1987 edition of the Scientific Information Display Digest, an article titled Fluorescent Indicator Panel with Simple Diode Construction by Masanobu Yamaguchi, Kazuo Kaneko, and Hirokichi Seo disclosed an experimental flat diode structure for use in a flourescent indicator panel. The diode structure used a tungsten cathode filament of one micron in thickness to provide electron emissions to a phosphor screen. A noted disadvantage was that the power consumption of the cathode filament was too high for practical application. Furthermore, because of the thermal diffusion of the cathode filament, the electrical pulse time of the diode structure was, at a minimum, 3 milliseconds. The electrical pulse time is the amount of time in which a thermal source is applied to the cathode filament to generate an electron emission. Electrical pulse times of 3 milliseconds are unsuitably high for most display purposes. The article concluded that the flat diode was impractical to be used as a display because the power consumption of the filament was too great and the pulse time of the emission was too high.
Thus, it would be an advancement in the art to provide a display device which produces high quality monochrome or color images over a broader range of display sizes yet requires less space and power for implementation.
It would be another advancement in the art to provide a display device which is operable in high temperatures and high radiation conditions.
It would be yet another advancement in the art to provide a display device which is relatively easy to manufacture, practical, reliable, and reproducible.
It would be a further advancement in the art to provide a display device incorporating electron emission principles while eliminating previous limitations.
Such an invention is disclosed and claimed herein.